Observable actions of algebraic groupsResearch Paper
Motivation
Let G be an affine algebraic group and let X be an affine algebraic variety. An action is called observable if for any G-invariant, proper, closed subset Y of X there is a nonzero invariant such that f(Y) =0. We characterize this condition geometrically as follows. The action is observable if and only if (1) there is a nonempty open subset consisting of closed orbits, and (2) the field of G-invariant rational functions on X is equal to the quotient field of . In case G is reductive, we conclude that there exists a unique, maximal, G-stable, closed subset of such that is observable. Furthermore, the canonical map is finite and bijective.
This mission is the statement-level formalization of Observable actions of algebraic groups (arXiv:0902.0137v2). Every numbered result of the paper was scanned. The results stated here are open sorry goals, ready for solvers to prove.
What is formalized
8 statements of the paper are in Lean 4 (Mathlib 0df444a). The goal theorem is Observability, invariant rational functions, and generic closed orbits (Abstract main characterization; Theorem 3.10, PDF p. 1). The milestones are the other numbered results, in the paper's order, each quoting the paper.
The paper's own objects are the definition item of this mission. Objects shared across papers come from the prove2quantum library and from earlier papers' missions, listed as references.
Provenance: prove2quantum's pipeline drafted each statement (gpt-6.1-sol on Stanford's Sherlock cluster). A blind read-back, written without seeing the paper, is attached to every item. An independent moderator compared each statement against the paper and passed the whole paper without edits.
Deferred results
12 results of the paper are not stated yet, because the library lacks an interface they need:
- §1, unnumbered: left and right translation observability: Closed algebraic subgroup, homogeneous-space geometric quotient, and quasi-affineness (hard)
- §1, unnumbered main result: finite purely inseparable socle quotient: Reductive group, computed socle, canonical restriction of invariant algebras, and finite socle quotient morphism (hard)
- Proposition 2.7: Characteristic-free algebraic unipotence and universal quantification over affine actions (hard)
- Proposition 3.2: A valid reduced/reducible six-way equivalence (source obstruction) (source-ambiguity)
- Proposition 3.13: Characteristic-free reductive and unipotent algebraic groups and regular direct product (hard)
- Proposition 3.17: Genuine contracted product G*_H X with geometric quotient sheaf and induced G-action (hard)
- Theorem 3.18: Full geometric quotient property for the canonical localized affine quotient (hard)
- Lemma 4.3: Reductive categorical quotient with canonical map on geometric points (hard)
- Lemma 4.5: Reductive categorical quotient and restriction to the nonmaximal locus (hard)
- Theorem 4.6: Reduced stable subvariety restriction, reductive categorical quotient, socle and canonical invariant-field map for possibly reducible Z (hard)
- Theorem 4.7: Computed socle as a reduced stable subvariety with its induced action, plus reductivity (hard)
- Proposition 4.8: Computed socle vanishing ideal and arbitrary-characteristic reductivity (hard)
Selected references
- Observable actions of algebraic groups, arXiv:0902.0137v2, https://arxiv.org/abs/0902.0137v2